Elastomeric riser tensioner system

Abstract

A riser tensioner system for applying a substantially constant tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of the riser. The system includes a plurality of tensioner assemblies each of which are coupled to the riser and to the platform. Each of the tensioner assemblies includes an upper member, a lower member, a connecting member coupled to the upper and lower members, and intermediate members coupled to the upper and lower members at a point intermediate the ends of the upper and lower members. At least one of the upper member, the lower member, and the intermediate members are adapted to provide a constant tensioning force. The arrangement of the upper member, lower member, connecting member, and intermediate members further provide a linkage whose centerline in angularly spaced from the longitudinal axis of the riser by a substantially constant amount throughout the range of motion of the linkage.

What is claimed is: 
     
       1. A riser tensioner system for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser, said system comprising: a plurality of tensioner assemblies, wherein each of said tensioner assemblies are coupled to said riser and to said platform, and wherein each of said tensioner assemblies comprises: an upper member including a first end and a second end, said first end of said upper member coupled to said floating platform;   a lower member including a first end and a second end, said second end of said lower member coupled to said riser;   a connecting member coupled to said second end of said upper member and said first end of said lower member; and   an intermediate member coupled to said upper member at a point intermediate said first and second ends of said upper member and to said lower member at a point intermediate said first and second ends of said lower member;     wherein at least one of said upper member, said lower member, and said intermediate member are adapted to provide a tensioning force.   
     
     
       2. The riser tensioner system of claim 1, wherein said upper member is adapted to provide a tensioning force. 
     
     
       3. The riser tensioner system of claim 2, wherein said upper member comprises: an outer canister coupled to said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.   
     
     
       4. The riser tensioner system of claim 3, wherein said columnar stack of compression elements comprises: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       5. The riser tensioner system of claim 4, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       6. The riser tensioner system of claim 5, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       7. The riser tensioner system of claim 3, wherein said outer canister of said upper member is pivotally connected to said intermediate member, and wherein said inner canister of said upper member is pivotally connected to said connecting member. 
     
     
       8. The riser tensioner system of claim 3, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said upper member and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       9. The riser tensioner system of claim 8, wherein said piston of said upper member is pivotally connected to said floating platform, and wherein said lower member is pivotally connected to said riser. 
     
     
       10. The riser tensioner system of claim 1, wherein said intermediate member is adapted to provide a tensioning force. 
     
     
       11. The riser tensioner system of claim 10, wherein said intermediate member comprises: an outer canister coupled to said upper member and defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   a piston positioned within said chamber and coupled to said lower member, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       12. The riser tensioner system of claim 11, wherein said columnar stack of compression elements comprises: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       13. The riser tensioner system of claim 12, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       14. The riser tensioner system of claim 13, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       15. The riser tensioner system of claim 11, wherein said piston of said intermediate member is pivotally connected to said lower member, and wherein said outer canister of said intermediate member is pivotally connected to said upper member. 
     
     
       16. The riser tensioner system of claim 10, wherein said intermediate member comprises: an outer canister defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   an upper piston positioned within said chamber and coupled to said upper member, said upper piston adapted for compressing a portion of said columnar stack of compression elements; and   a lower piston positioned within said chamber and coupled to said lower member, said lower piston adapted for compressing another portion of said columnar stack of compression elements.   
     
     
       17. The riser tensioner system of claim 16, wherein said columnar stack of compression elements comprises: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       18. The riser tensioner system of claim 17, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       19. The system, as set forth in claim 18, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       20. The riser tensioner of claim 16, wherein said upper piston of said intermediate member is pivotally connected to said upper member, and wherein said lower piston of said intermediate member is pivotally connected to said lower member. 
     
     
       21. The riser tensioner system of claim 1, wherein said lower member is adapted to provide a tensioning force. 
     
     
       22. The riser tensioner system of claim 21, wherein said lower member comprises: an outer canister coupled to said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.   
     
     
       23. The riser tensioner system of claim 22, wherein said columnar stack of compression elements comprises: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       24. The riser tensioner system of claim 23, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and 4 complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       25. The riser tensioner system of claim 24, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       26. The riser tensioner system of claim 22, wherein said outer canister of said lower member is pivotally connected to said intermediate member, and wherein said inner canister of said lower member is pivotally connected to said connecting member. 
     
     
       27. The riser tensioner system of claim 22, wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said lower member and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       28. The riser tensioner system of claim 27, wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       29. The riser tensioner system of claim 1, wherein said upper member and said lower member are adapted to provide a tensioning force. 
     
     
       30. The riser tensioner system of claim 29, wherein said upper member comprises: an outer canister coupled to said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters; and   wherein said lower member comprises: an outer canister coupled to said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and     a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.   
     
     
       31. The riser tensioner system of claim 30, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       32. The riser tensioner system of claim 31, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       33. The riser tensioner system of claim 32, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       34. The riser tensioner system of claim 30, wherein said outer canisters of said upper and lower members are pivotally connected to said intermediate member, and wherein said inner canisters of said upper and lower members are pivotally connected to said connecting member. 
     
     
       35. The riser tensioner system of claim 30, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said upper member and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements; and   wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said lower member and coupled to said riser, said piston adapted for compressing said columnar stack of compression elements.     
     
     
       36. The riser tensioner system of claim 35, wherein said piston of said upper member is pivotally connected to said floating platform, and wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       37. The riser tensioner system of claim 1, wherein said intermediate member and said lower member are adapted to provide a tensioning force. 
     
     
       38. The riser tensioner system of claim 37, wherein said intermediate member comprises: an outer canister coupled to said upper member, said outer canister further defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   a piston positioned within said chamber adapted for compressing said columnar stack of compression elements; and   wherein said lower member comprises: an outer canister coupled to said piston of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.     
     
     
       39. The riser tensioner system of claim 38, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       40. The riser tensioner system of claim 39, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       41. The riser tensioner system of claim 40, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       42. The riser tensioner system of claim 38, wherein said piston of said intermediate member is pivotally connected to said outer canister of said lower member, and wherein said outer canister of said intermediate member is pivotally connected to said upper member. 
     
     
       43. The riser tensioner system of claim 38, wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters and coupled to said riser, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       44. The riser tensioner system of claim 43, wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       45. The riser tensioner system of claim 37, wherein said intermediate member comprises: an outer canister defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   an upper piston positioned within said chamber and coupled to said upper member, said upper piston adapted for compressing a portion of said columnar stack of compression elements; and   a lower piston positioned within said chamber adapted for compressing another portion of said columnar stack of compression elements; and   wherein said lower member comprises: an outer canister coupled to said lower piston of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and     a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.   
     
     
       46. The riser tensioner system of claim 45, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       47. The system, as set forth in claim 46, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       48. The system, as set forth in claim 47, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       49. The riser tensioner of claim 45, wherein said lower piston of said intermediate member is pivotally connected to said outer canister of said lower member, and wherein said upper piston of said intermediate member is pivotally connected to said upper member. 
     
     
       50. The riser tensioner system of claim 45, wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters and coupled to said riser, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       51. The riser tensioner system of claim 50, wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       52. The riser tensioner system of claim 1, wherein said intermediate member and said upper member are adapted to provide a tensioning force. 
     
     
       53. The riser tensioner system of claim 52, wherein said intermediate member comprises: an outer canister defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   a piston positioned within said chamber and coupled to said lower member, said piston adapted for compressing said columnar stack of compression elements; and   wherein said upper member comprises: an outer canister coupled to said outer canister of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.     
     
     
       54. The riser tensioner system of claim 53, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       55. The riser tensioner system of claim 54, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       56. The system, as set forth in claim 55, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       57. The riser tensioner system of claim 53, wherein said outer canister of said intermediate member is pivotally connected to said outer canister of said upper member, and wherein said piston of said intermediate member is pivotally connected to said lower member. 
     
     
       58. The riser tensioner system of claim 53, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       59. The riser tensioner system of claim 58, wherein said piston of said upper member is pivotally connected to said floating platform. 
     
     
       60. The riser tensioner of claim 52, wherein said intermediate member comprises: an outer canister defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   an upper piston positioned within said chamber adapted for compressing a portion of said columnar stack of compression elements; and   a lower piston positioned within said chamber and coupled to said lower member, said lower piston adapted for compressing another portion of said columnar stack of compression elements; and   wherein said upper member comprises: an outer canister coupled to said upper piston of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and     a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.   
     
     
       61. The riser tensioner system of claim 60, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       62. The riser tensioner system of claim 61, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       63. The riser tensioner system of claim 62, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       64. The riser tensioner system of claim 60, wherein said upper piston of said intermediate member is pivotally connected to said outer canister of said upper member, and wherein said lower piston of said intermediate member is pivotally connected to said lower member. 
     
     
       65. The riser tensioner system of claim 60, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements.   
     
     
       66. The riser tensioner system of claim 65, wherein said piston of said upper member is pivotally connected to said floating platform. 
     
     
       67. The riser tensioner system of claim 1, wherein said upper member, said intermediate member, and said lower member are adapted to provide a tensioning force. 
     
     
       68. The riser tensioner system of claim 67, wherein said upper member comprises: an outer canister;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters;   wherein said intermediate member comprises: an outer canister defining a chamber and coupled to said outer canister of said upper member;   a columnar stack of compression elements contained within said chamber defined by said outer canister of said intermediate member; and   a piston positioned within said chamber defined by said outer canister of said intermediate member adapted for compressing said columnar stack of compression elements; and     wherein said lower member comprises: an outer canister coupled to said piston of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and     a columnar stack of compression elements, contained within a chamber defined by said inner and outer canisters.   
     
     
       69. The riser tensioner system of claim 68, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       70. The riser tensioner system of claim 69, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       71. The riser tensioner system of claim 70, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       72. The riser tensioner system of claim 68, wherein said outer canister of said intermediate member is pivotally connected to said outer canister of said upper member, and wherein said outer canister of said lower member is pivotally connected to said piston of said intermediate member. 
     
     
       73. The riser tensioner system of claim 68, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said upper member and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements; and   wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said lower member and coupled to said riser, said piston adapted for compressing said columnar stack of compression elements.     
     
     
       74. The riser tensioner system of claim 73, wherein said piston of said upper member is pivotally connected to said floating platform, and wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       75. The riser tensioner system of claim 67, wherein said upper member comprises: an outer canister;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters;   wherein said intermediate member comprises: an outer canister defining a chamber;   a columnar stack of compression elements contained within said chamber defined by said outer canister; and   an upper piston positioned within said chamber and coupled to said outer canister of said upper member, said upper piston adapted for compressing a portion of said columnar stack of compression elements; and   a lower piston positioned within said chamber adapted for compressing another portion of said columnar stack of compression elements; and     wherein said lower member comprises: an outer canister coupled to said lower piston of said intermediate member;   an inner canister coupled to said connecting member, said inner canister positioned within and extending from said outer canister; and   a columnar stack of compression elements contained within a chamber defined by said inner and outer canisters.     
     
     
       76. The riser tensioner system of claim 75, wherein each said columnar stack of compression elements comprise: a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having: an inner flange having a curved outer coupling portion;   an outer flange having a curved inner coupling portion;   a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and   at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least on curved reinforcement share a common focal point along a central cross-section;     wherein said top compression element is coupled to said outer cylindrical member and said bottom compression element is coupled to said center rod, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.   
     
     
       77. The system, as set forth in claim 76, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member. 
     
     
       78. The system, as set forth in claim 77, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub. 
     
     
       79. The riser tensioner system of claim 75, wherein said upper piston of said intermediate member is pivotally connected to said outer canister of said upper member, and wherein said outer canister of said lower member is pivotally connected to said lower piston of said intermediate member. 
     
     
       80. The riser tensioner system of claim 75, wherein said upper member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said upper member and coupled to said floating platform, said piston adapted for compressing said columnar stack of compression elements; and   wherein said lower member further comprises: a piston positioned within said chamber defined by said inner and outer canisters of said lower member and coupled to said riser, said piston adapted for compressing said columnar stack of compression elements.     
     
     
       81. The riser tensioner system of claim 80, wherein said piston of said upper member is pivotally connected to said floating platform, and wherein said piston of said lower member is pivotally connected to said riser. 
     
     
       82. The riser tensioner system of claim 1, wherein said connecting member is pivotally connected to said upper and lower members. 
     
     
       83. The riser tensioner system of claim 1, wherein said intermediate member is pivotally connected to said upper and lower members. 
     
     
       84. The riser tensioner system of claim 1, wherein said connecting member is pivotally connected to said upper and lower members, and wherein said intermediate member is pivotally connected to said upper and lower members. 
     
     
       85. A riser tensioner system for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser, said system comprising: a plurality of tensioner assemblies, wherein each of said tensioner assemblies is coupled to said riser and to said floating platform, and wherein each of said tensioner assemblies comprises: a first member including a first end and a second end, said first end of said first member being coupled to said floating platform;   a second member including a first end and a second end, said second end of said second member being coupled to said riser;   a connecting member coupled to said second end of said first member and said first end of said second member; and   an intermediate member coupled to said first member at a point intermediate said first and second ends of said first member and to said second member at a point intermediate said first and second ends of said second member;     wherein at least one of said first member, said second member, and said intermediate member is adapted to provide a tensioning force.   
     
     
       86. The riser tensioner system as claimed in claim 85, wherein said second end of said first member is pivotally connected to said connecting member, said first end of said second member is pivotally connected to said connecting member, and said connecting member is bisected by a centerline of said each of said tensioner assemblies. 
     
     
       87. The riser tensioner system as claimed in claim 85, wherein said second end of said first member is pivotally connected to said connecting member, said first end of said second member is pivotally connected to said connecting member, and said connecting member rotates about a centerpoint of said connecting member when said floating platform moves within a given range along a longitudinal axis of said riser. 
     
     
       88. The riser tensioner system as claimed in claim 85, wherein said connecting member is substantially perpendicular to said first member and to said second member. 
     
     
       89. A tensioner assembly for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser when said tensioner assembly is coupled to said riser and to said floating platform, said tensioner assembly comprising: a first member including a first end and a second end, said first end of said first member being adapted for coupling to said floating platform;   a second member including a first end and a second end, said second end of said second member being adapted for coupling to said riser;   a connecting member coupled to said second end of said first member and said first end of said second member; and   an intermediate member coupled to said first member at a point intermediate said first and second ends of said first member and to said second member at a point intermediate said first and second ends of said second member;   wherein at least one of said first member, said second member, and said intermediate member is adapted to provide a tensioning force.   
     
     
       90. The tensioner assembly as claimed in claim 89, wherein said second end of said first member is pivotally connected to said connecting member, said first end of said second member is pivotally connected to said connecting member, and said connecting member is bisected by a centerline of said tensioner assembly. 
     
     
       91. The tensioner assembly as claimed in claim 89, wherein said second end of said first member is pivotally connected to said connecting member, said first end of said second member is pivotally connected to said connecting member, and said connecting member rotates about a centerpoint of said connecting member when said tensioner assembly is coupled to said riser and to said floating platform and said floating platform moves within a given range along a longitudinal axis of said riser. 
     
     
       92. The tensioner assembly as claimed in claim 85, wherein said connecting member is substantially perpendicular to said first member and to said second member.